Silver tetrafluoroborates, reaction with

Complex 105 enters the pyrazoleAriphenylphosphine ligand substitution reaction with PPha to give 108 (910M3123). Further reaction with triphenylphosphine and silver tetrafluoroborate gives the heterodinuclear complex 109 (94IC2196). 

The N-coordinated compound [AuCljL] (L= l-ethyl-2-phenylimidazole) with silver tetrafluoroborate gives the cycloaurated species 102, which on further reaction with triphenylphosphine and sodium tetrafluoroborate or ammonium hexafluorophosphate forms the cationic complexes 103 (X = BF., PF,) (00JCS(D)271). 

Chiral alcohols have also been used in an asymmetric synthesis of sulphoxides based on halogenation of sulphides. Johnson and coworkers have found319 that the reaction of benzyl p-tolyl sulphide with JV-chlorobenzotriazole (NCBT) followed by addition of (—) menthol and silver tetrafluoroborate afforded diastereoisomeric menthoxysulphonium salts 267 which, upon recrystallization and hydrolysis, gave benzyl p-tolyl sulphoxide with 87% optical purity (equation 145). More recently, Oae and coworkers reported320 that optically active diaryl sulphoxides (e.e. up to 20%) were formed either by hydrolysis or thermolysis of the corresponding diaryl menthoxysulphonium salts prepared in situ from diaryl sulphides using ( —) menthol and t-butyl hypochlorite. 

Bis[Ar,Ar -di(2-pyridyl)- and -di(2-pyridyl-methyl)-imidazol-2-ylidene]aurate(i) tetrafluoroborates have been prepared from the analogous silver complexes on reaction with (tht)AuCl and their structures determined. The configuration of the cations with sterically well-protected two-coordinate gold centers shows no anomalies. However, fascinating structures are found for the adducts with silver tetrafluoroborate obtained as acetonitrile... 

In their important work on the synthesis and properties of optically active chlorosulfurane (+)-177, Martin and Balthazor (195) deduced its absolute configuration by means of chemical correlations. Reaction of (+)-l 77 with silver tetrafluoroborate yields cyclic sulfonium salt 198, which was hydrolyzed without isolation under alkaline conditions to give sulfoxide (-)-(5 -180, from which (+)-177 was obtained. Assuming that the conversion (+)-l 77 -> 198 proceeds with... 

That only the wrong C-16 diastereomer seemed to be produced in this reaction was then demonstrated by the Kutney group, who prepared a series of binary indole-indoline alkaloids using the chloroindolenine approach. The apparent simplicity of this coupling reaction and the rapidity in assembling such binary alkaloids prompted an extensive study of reaction conditions (28), with the desire to find a procedure suitable for generation of the C-16 (S) isomer, required for anticancer activity. Despite the intensive effort involved in this in-depth study, no success could be realized, and it was therefore widely accepted that .. . it is very unlikely that any natural dimer could be obtained in this way (7). At this point it may be noted, however, that we were able to show subsequently that the desired C-16 -C-14 PARF relative stereochemistry can be obtained as a preferential result, albeit only in very low yield [3.6% PARF versus 2.1% PREF (priority reflective)], when the chloroindolenine reaction with vindoline is initiated with silver tetrafluoroborate (13). 

Chlorination of these vinylogous urethanes 152 with r rt-butylhypochlo-rite, followed by reaction with silver tetrafluoroborate and protonated vindoline, at or below room temperature, provided almost exclusively coupling products 157 and 158 with the desired C-16 -C-14 PARF rela-... 

Conversion of the resulting separate D-seco D-E trans i-vincadiffor-mine diols 198-201 to their primary tosylates and tertiary trimethylsilyl-oxy derivatives 202-205 and coupling to vindoline by the chlorination-silver tetrafluoroborate-potassium borohydride sequence provided amino tosylates 206-209, which could be directly subjected to cyclization or, alternatively, converted to the C-20 -C-21 epoxides 178, 181, 210, and 211 by reaction with tetrabutylammonium fluoride (Scheme 53). While cyclization of the tosylates 206-209 led essentially only to quaternary salts which could be debenzylated to provide the lower energy atropi-somer of vinblastine (1), leurosidine (56), vincovaline (184), and its C-20 epimer (212) respectively, cyclization of the epoxides 178, 181, 210, and... 

The primary advantage in the first step of the method described here (using 1-chlorobutane diluted in MeCN) is that it eliminates long reaction periods and allows the use of secondary alkyl halides without competitive elimination reactions. For example, the reaction of sec-butyl bromide with N-methylimidazole using the classical method (in neat alkyl halide) produces, along with the desired product, 20-30% of butenes and 1-methylimidazole hydrobromide. In the second step, the use of water as solvent allows the anion metathesis reaction to be quantitative in a very short time and allows the easy purification of the ionic liquids. Moreover, employing the potassium salt avoids the use of corrosive and difficult to handle hexafluorophosphoric add and the expensive silver tetrafluoroborate. ... 

The first asymmetric synthesis of (-)-monomorine I, an enantiomer of the natural alkaloid, by Husson and co-workers starts with the chiral 2-cyano-6-oxazolopiperidine synthon (385) prepared from (-)-phenylglycinol (384), glu-taraldehyde (383), and KCN (443). Alkylation of 385 with an iodo ketal led to the formation of a single product (386). The cyano acetal (386) was treated with silver tetrafluoroborate and then zinc borohydride to afford a 3 2 mixture of C-6 epimeric oxazolidine (387) having the (2S) configuration. Reaction of 387 with... 

The reactions of chlorosilicon and chlorogermanium transition metal complexes with silver hexafluoroantimonate, as well as with silver tetrafluoroborate or silver hexafluorophosphate. 

Exchange-Fluorination by Reaction with Silver(I) Tetrafluoroborate General Procedure 70... 

There was particular interest in the analogous reactions of 1-Oacetyl-2,3,5-tri-0-benzoyl-4-bromo-/ -D-ribose (37), because of the potential to prepare from it compounds related to nucleocidin, which is a 4 -fluoroaden-osine derivative having antitrypanosomal activity. With silver fluoride in acetonitrile, this bromide also reacted mainly with inversion of configuration, and gave the l-lyxo fluoride 140 (53% isolated yield), whereas, with silver tetrafluoroborate, much more of the more interesting 1-0-acetyl-2,3,4-tri-0-benzoyl-4-fluoro-/ -D-ribose (141) was obtained.38... 

Several examples of the cyclization of indole derivatives with alkenic side chains in the 3-position have been reported.6 In these examples, palladium chloride in combination with silver tetrafluoroborate is the cyclizing agent. The palladium tetrafluoroborate, presumably formed, should be a very reactive palladating species and probably is the reason why these reactions proceed at room temperature, although the mechanism is not yet completely clear. These reactions were worked up reductively (by addition of sodium borohydride) in order to reduce the expected alkenic product or any relatively stable organopalladium complexes that may have been formed (equation 4).6... 

Methyl a-arylalkanoates. Treatment of methyl ketals of a-halogenoalkyl aryl ketones, prepared in situ, with a number of silver salts, particularly silver tetrafluoroborate or hexafluoroantimonate, in methanol induces a rearrangement to methyl a-arylalkanoates in yields generally around 98%. The rate is influenced by substituents on the aryl group, the oxygens of the ketal group greatly facilitate this reaction (equation I).1... 

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